A 2000 PA Ultra should be just a tiny bit slower than the 99 SSEi, just for the fact that the 92-99 Bonnies were lighter.
Comparing it to a 00+ Bonnie though and you lose some of that weight difference.
I think Rogue told me his 00+ SSEi weighed 3880lbs. and my 98 Ultra is 3905lbs.
The 97+ PA and 00+ Bonnie share suspensions and the Ultra ususally has the same F41 top-option suspension that the SSEi has, but with slightly softer shocks. The Ultra won't be quite as fast in the corners as the SSEi, but you won't be disappointed by the handling, either. Check your RPO codes on the underside of the spare-tire cover.
As for acceleration, I managed a 15.36 in the 1/4 in my Ultra, back when it was stock.
Trust me, if you like the Bonnie, you won't be let down by the PA.